The present invention relates to a water based well servicing fluid, additives therefore, and to a process for preparing the same. More particularly, the present invention relates to the formation and use of an improved drilling fluid which includes a sulfonated amino-aldehyde, methyl cellulose and/or polyvinyl alcohol.
In well drilling, a drilling fluid or mud is pumped down through the drill stem of the rotary rig, circulated around the drill bit and returned to the surface through the annular passage between the drill stem and the well wall. The drilling fluid lubricates the drill stem and bit, cools the bit and carries the cuttings from the bit up to the surface. The drilling fluid also provides a hydrostatic head against the walls of the well to contain downhole geopressure.
In drilling for oil, gas or water there are generally three zones. The first zone ranges from 0-5000 feet, while the second and third zones range from 5000 to 7000 feet and greater than 7000 feet respectively.
During the initial stage of drilling, i.e. the first zone of the well, a relatively large bore hole is usually desired. In other words, a relatively large quantity of drill cuttings must be moved to the surface. This requires a well servicing fluid with excellent carrying capacity as indicated by a high yield point which ranges from 20-30 pounds per 100 square feet and a plastic viscosity of 3-6 centipoise.
As the drilling operation gets deeper, smaller bore holes are drilled resulting in smaller amounts of cuttings. However, the drilling fluid travels longer distances under higher pressure and is subjected to higher temperatures.
During these drilling operations, the drilling fluid is monitored and adjusted to obtain the desired characteristics at various depths and under varying conditions. For example, there are three fluid properties which are monitored. These three properties are viscosity, yield point and fluid loss. And in general, it is desirable to maintain these properties constant over the longest possible duration. It is also desirable to use additives which are compatible with other materials in the drilling fluid, to use thermally stable non-toxic additives, to avoid excessive usage and to prevent environmental pollution.
A wide variety of drilling fluids have been used. For example, clay based drilling fluids have been used for cooling and particle removal. In fact, the U.S. Pat. No. 4,519,923 discloses the use of sodium carboxymethyl cellulose as a water loss reducing agent to be included in drilling mud. Hori also discloses the use of sulfoethylcellulose alkali metal salts as a water loss reducing agent.
In addition, the U.S. Pat. No. 3,872,018 discloses a fluid loss control at temperatures over 300.degree. F. in clay-free sea water muds by the addition of polyvinyl alcohol with starch and that urea with the polyvinyl alcohol further increases temperature stability. As stated in that patent 2 to about 10 pounds per barrel of polyvinyl alcohol is sufficient. And, the average molecular weight of the polyvinyl alcohol ranges from at least about 170,000 to over 200,000.
Another approach for a High Temperature Stable Fluid Loss Control System is disclosed by Green U.S. Pat. No. 4,473,480. Green discloses a combination of (a), silicate or alumino silicate material; (b) a chemical compound capable of converting to a higher oxidation state under alkaline conditions; and, (c) a reaction product formed between a polymeric material selected from polyvinyl alcohol or hydroxyalkyl cellulose and a cross linking agent. Green discloses reacting a polyvinyl alcohol having an average molecular weight of between 90,000 to 200,000 with an aldehyde such as formaldehyde or melamine formaldehyde.